Polyarylene sulfides (hereinafter abbreviated to “PAS”) such as polyphenylene sulfide (hereinafter abbreviated to “PPS”) has excellent heat resistance and chemical resistance, and is widely used for electric/electronic components, car components, water heater components, fibers, and films. In these respective applications, PAS having a high molecular weight is particularly highly desired in recent years in terms of the strength and moldability. PAS having a high molecular weight is generally produced by synthesizing PAS having a low molecular weight and subsequently subjecting it to thermally oxidative cross-linking. This PAS whose molecular weight is increased by the thermally oxidative cross-linking is usually difficult to be subjected to melt extrusion molding, and the application thereof has been limited.
Therefore, as a method for producing the linear PAS having a high molecular weight, for example, the method is known, in which a hydrous alkali metal sulfide, N-methylpyrrolidone whose amount is less than 1 mol per mol of the hydrous alkali metal sulfide, and a polyhaloaromatic compound are mixed, the mixture is dehydrated by azeotropy to thereby obtain the composition containing a microparticulated anhydrous alkali metal sulfide in a slurry form, the slurry is heated and polymerized to produce a linear PAS having a high molecular weight with good production efficiency (refer to Patent Document 1).
The aforementioned method can suppress side reactions and efficiently produce a linear PAS having a high molecular weight. However, because the starting materials are polymerized by a heterogeneous reaction that reacts them in a slurry form, the reactivity is not sufficient, and the recently desired level of the high molecular weight is not achieved.
Meanwhile, as a method for producing PAS having a high molecular weight and high quality, the method is known, in which a dihalogenated aromatic compound and the alkali metal sulfide are reacted in the presence of a lithium compound in a substantially anhydrous condition (refer to Patent Document 2).
However, according to the method in which a dihalogenated aromatic compound and the alkali metal sulfide are reacted in the presence of a lithium compound in a substantially anhydrous condition, a very expensive lithium compound needs to be used in a large amount, and therefore, this method is not economical in terms of industrial manufacture and is difficult to be turned into practical use. In addition, the reaction time is long, and the pressure inside the reaction system is extremely high. Therefore, PAS cannot be efficiently produced.
Patent Document 1
    Japanese Unexamined Patent Application, First Publication No. Hei 8-231723Patent Document 2    Japanese Unexamined Patent Application, First Publication No. Sho 62-253622